The present invention relates to a valve for controlling flow rate of gas, and more particularly to a control valve proper for using in a discharge system and a supply system in a system for manufacturing semiconductors, liquid crystals and others, in particular to a control valve having an emergency cutout mechanism.
In the discharge system of the semiconductor manufacturing system, a needle control valve used for controlling the flow rate of gas. The needle valve is linearly operated by a diaphragm under the condition of a positioning device, or by a screw rotated by a motor.
In the discharge system of the semiconductor manufacturing system, when power supply is cut off without warning in discharge operation by a pump under the controlling of the opening of a passage by the control valve, atmosphere runs back from the stopped pump passing through the passage. As a result, the pressure in the passage quickly increases, so that particles accumulated in the passage are raised and fed to a reaction furnace to contaminate the furnace. In an emergency stop of the pump other than the cut off power, the same trouble as the above occurs.
Therefore, it is necessary to quickly close the control valve at such an emergency in order to prevent the occurrence of the trouble.
However, in the conventional flow rate control valve, an actuator for operating the valve becomes inoperative when the power supply is cut off. About the emergency stop of the pump, no measure is provided. Consequently, the contamination of the reaction furnace can not be prevented, and the furnace must be cleaned, which causes the resumption of manufacturing to delay even if the power is supplied.
It may be considered that an uninterruptible power supply system (UPS) is employed in order to resolve the above described problem. The UPS detects the power cutoff, and supplies power from a battery for several minutesxe2x80x94several tens minutes to operate the actuator of the control valve, thereby closing the valve. However, about two minutes elapse before the closing of the valve, during which the reaction furnace may be polluted.
On the other hand, even if the UPS is provided, the control valve is not closed when the battery is broken, the breaker of the distributor fails, or the wiring is broken.
An object of the present invention is to provide a control valve which may be urgently and securely closed at an emergency so that the manufacturing operation can be continued without stopping.
According to the present invention, there is provided a valve for controlling flow rate of gas comprising a valve body having a passage including a hole in which gas flows, a valve for closing the hole, an actuator including a slider for operating the valve, an emergency cutoff device connected to the valve and releasably connected to the actuator releasing means for releasing the emergency cutoff device from the actuator in an emergency, urging means for urging the valve to the hole when releasing of the emergency cutoff device.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.